This invention relates to laminates of phenolic resins coated with a finishing layer to remove surface irregularities.
Laminates comprising several successive layers of fiber reinforced phenolic resins are known in the art. They are described, for example, in the "Encyclopedia of Polymer Science and Technology", Interscience Publishers, 1970, V. 12, page 1 "Reinforced Plastics" and V. 8, page 121 "Laminates". Glass fibers are the preferred reinforcing agents. A composite material of this type in the majority of cases shows, at the surface, imprints of insufficiently impregnated fibers. If attempts are made to mask these surface flaws by directly applying a coating to the laminate, for example, a coating based on a polyurethane binder, the surface appearance of the material obtained remains poor and a smooth surface is not achieved.
To overcome these disadvantages it has been proposed to initiate the production of the laminate by applying directly onto the mold, provided with a mold release agent, a layer of a non-reinforced resin, this layer usually being referred to as a "gel coat". This layer adheres to the laminate and may, where appropriate, form a supporting layer for, e.g., a coat of paint. However, depending on the resins employed to produce the "gel coat", the results obtained are not satisfactory. Thus, for example, there have been proposed "gel coats" of phenolic resin for coating glass fiber-reinforced phenolic laminates; in that case, the surface obtained exhibits micro-pitting and the imprint of the fibers. The micro-pitting and the outline of the fibers can be removed by depositing a thicker layer of phenolic resin but in that case the appearance of micro-crazing or crackling is observed. It has also been proposed to use a "gel coat" of unsaturated polyester resin; in that case, the surface hardness obtained is inadequate.
In order to solve all these problems and in particular to obtain laminates which exhibit neither crackling nor micro-crazing and have good hardness, it has been proposed to coat laminates based on phenolic resin with a furan-based "gel coat", U.S. Pat. No. 4,283,462 issued Aug. 11, 1981. Unfortunately, the materials so coated have the disadvantage of being dyed in the color of the furan resins, namely black. It is therefore necessary to coat them with another thermosetting resin suitably pigmented, if a material exhibiting a different color is required.